XRAY - Model racing cars

What do i need to change to reduce grip roll? I race indoors on carpet using rubber tyres. The beginning of the session is fine but towards the end and in the finals the grip comes right up due to the additive being left on the carpet. I've glued the sidewalls of the tyres and this has helped a little i've also tried running without any additive in the last races but still get grip roll. This happens on both my 009 and my sons fk05, my 009 is set up as per book my sons is set up as per Martin hudy's carpet / rubber.Any suggestions please.